Method of eliminating hum in pushpull circuits



Feb. 16, 1937. A, c. ANSLEY 2,070,772

METHOD OF ELIMINATING HUM IN PUSH-PULL CIRCUITS Filed Jan. 26, 1935 INVENTOR ART/{0P CIA/V5415) BY AI'TORNEY Patented Feb. 16, 1931 2,070,772

UNITED STATES PATENT OFFICE METHOD OF ELIIVIINATING HUM IN PUSH- PULL CIRCUITS Arthur C. Ansley, New York, N. Y. Application January 26, 1935, Serial No. 3,573 1 Claim. (01. 179-171) This invention relates to a system of ampli- In carrying out the present invention I provide fication in radio circuits using tetrode or pentode means whereby the current delivered to the pritubes in push-pull relation. mary Ill by the plates of each tube may be equal- An object of the invention is to eliminate the ized and instead of connecting the screens directly 3 hum which is sometimes impressed upon the reto the source of positive voltage, as is usual, I ceiver when a pulsating current is used in supplyinterpose a resistance It in each of the leads ing the system. from the screens to the source of positive voltage It frequently happens that the tubes used in and I provide a movable arm or variable tap 20 the push-pull circuit do not have identical charconnected to the positive voltage of the current acteristics and the amount of current supplied supply. As each tap 20 is moved along each re- 10 to the primary coil of the output transformer sistance l8 the current drawn by the screens by the plate of one tube is not the same as the causes a variation in the voltage drop across current supplied by the plate of the other tube. the resistance and thereby causes a variation in A feature of the present invention relates to the voltage applied to each screen. This permits a method by which the hum impressed upon a a point to be found where the plate current of 15 receiver of a radio set of the type above described the two tubes may be equal and the hum resulting is eliminated, which consists in varying the from an otherwise unbalanced condition in a screen voltage to thereby equalize the plate curpush-pull circuit may be eliminated. rent in the tubes. In the form shown in Figure 2, a pentode tube The invention will be better understood by refis shown, which tube difiers from the tetrode. 20 erence to the following description and drawing tube of Figure 1 by the addition of a suppressor in whichgrid 2|. The principle of operation, however, is Figure 1 represents the last stage of amplificathe same as the Figure 1 arrangement except that tion in a push-pull circuit using tetrode tubes; a single resistance 22 is interposed between theand screens of the two tubes and a single movable 25 Figure 2 is a similar circuit using pentode tubes, arm or tap 20 is provided. This is connected to the connections in the latter figure being somethe source of positive voltage as in the Figure 1 what different from those shown in Figure 1. form.

Referring to the drawing, I designates the pri- By moving the tap along the resistance 22 the mary coil of the in-put transformer and 2 the portion of the resistance in series with one of 30 secondary coil thereof. The coil 2 is tapped at the screens may be reduced at the same time that its center and the tap is grounded at 3. 4, Figthe portion of resistance in series with the other ure 1, represents two electron tubes, the grids 6 screen is increased. In both forms the variaof which are connected to the ends of the section in the screen voltage operates to equalize the ondary 2. The plate 8 of each tube is connected. plate current in the tubes. 35

to the primary ID of the output transformer, What I claim is:- the mid point of which primary being connected A method of eliminating hum in the receiver to the positive terminal of a source of pulsating of a radio set using a pulsating current which current, as supplied by a rectifier tube in an set includes radio circuits having tubes of at least alternating current circuit. The secondary is, as four electrodes, said tubes arranged in push-pull 40 usual, connected in circuit with the loud speaker relation and the electrodes including a plate and a screen with supply circuits for each, which con- Each of the tubes 4 in Figure 1, in addition to sists in varying the screen voltage to equalize the grid and plate, includes a heating source [2, the plate current of the tubes while the pulsating a cathode l4 and a screen 16. The cathodes of current supply remains substantially constant. 45

the tube are connected together by a lead l5 connected to the negative side of a source of pul- ARTHUR C. ANSLEY. sating current through a resistor I1. 

